1. Technical Field
The present invention relates to an optical device that enlarges a luminous flux diameter in two directions, and a display apparatus that uses the optical device.
2. Related Art
In apparatuses that display images by performing scanning with light for the display of images, it is preferable that images are displayed with an optical device enlarging a luminous flux diameter in two directions, which mutually intersect one another. For example, in a retina scanning type projection type display apparatus, since a luminous flux used for scanning is caused to be incident via a pupil of an eye of a user from each angle direction, if the luminous flux diameter is small, it is not possible to cause a luminous flux used for scanning to be incident to a pupil of an eye of a user in a case where the positions of the eyes are shifted due to the interval between eyes differing for each user, or the like. Therefore, it is preferable to configure the apparatus so that a luminous flux is incident via a pupil hole of an eye with the luminous flux diameter enlarged even if the positions of the eyes are shifted.
Meanwhile, an element in which a light-transmissive layer and a partially reflective layer are alternately laminated has been suggested as an optical device, and according to such an element, it is possible to enlarge a luminous flux diameter of incident light in a direction in which the light-transmissive layer and the partially reflective layer are laminated (refer to JP-A-2006-301234). Furthermore, if optical devices as disclosed in JP-A-2006-301234, which are different in a direction in which the light-transmissive layer and the partially reflective layer are laminated, are disposed in series, enlargement of a luminous flux diameter in two directions intersecting each other can be achieved.
However, in a case in which two of the optical devices that are disclosed in JP-A-2006-301234 are disposed in series with different lamination directions of the light-transmissive layer and the partially reflective layer, there is a problem in that unevenness in optical intensity distribution and the like occurs if the partially reflective layer is configured from a dielectric multilayered film. That is, in a case in which a dielectric multilayered film that is used in a partially reflective layer is designed for S polarized light, since S polarized light that is emitted from an optical device in a previous stage becomes P polarized light with respect to an optical device in a latter stage, depending on an incidence angle, the transmittance is reduced greatly as a result of the influence of a Brewster angle, and therefore, unevenness in optical intensity distribution and the like occurs in emitted light. In particular, in a case in which the diameter of a luminous flux is enlarged after the luminous flux is used for scanning by a scanning unit, the abovementioned problem becomes more significant since light from a wide angular range is incident.